In an image forming system which includes a printing apparatus which forms an image onto a continuous web; and a web treatment apparatus which applies a specified treatment onto the web before or after printing, or a pre-treatment and post-treatment apparatus which reels out or reels in a roll-shaped web, there often exists multiple web conveying units on a web conveying path within the system. In this case, in general, a dancer roller apparatus is arranged so that an amount of slack of the web between a web conveying unit on the upstream side and a web conveying unit on the downstream side is absorbed and a proper tension is applied onto a web to be conveyed.
FIG. 7 is an overview configuration diagram showing one example of a flow of an inkjet image forming system.
In the system as shown, a web W, which is sent out from a paper-feeding apparatus 100, is sent into a treatment agent applying apparatus 101 and has applied onto an image forming face thereof a treatment agent which includes a function of coagulating ink before ink droplets impact on the web in order to solve problems such as blur, density, color tone, offset, etc. Depending on a desired printed matter, a face onto which a treatment agent is to be applied may be a single face or a double face.
Next, the web W is sent into a first inkjet printer 102, which ejects ink droplets on the front side of the web W, so that a desired image is formed thereon. Then, a front and a back of the web W are reversed by a turnover apparatus (not shown), and the web W is continuously sent into the second inkjet printer (not shown), ink droplets are ejected onto the back side of the web W, so that a desired image is formed. Then, the system is arranged such it is sent to a post-treatment apparatus in which a predetermined post-treatment is performed thereon.
FIG. 8, which is a schematic configuration diagram showing one example of the treatment agent applying apparatus 101 which is used in this image forming system, shows a state at the time the treatment agent is applied.
As shown, a large number of guide rollers 1, each having a bearing (not shown) at both ends thereof to be rotatably supported thereby, are arranged within the treatment agent applying apparatus 101 to secure a conveying path of the web W. A lead-in roller 2 is rotationally driven by a driving source (not shown) such as a motor and a nip roller 3 is pushed to the lead-in roller 2 side due to a pull tension of a spring (not shown). The lead-in roller 2 and the nip roller 3 may be rotated to lead in the web W from the paper-feeding apparatus 100 to inside this treatment agent applying apparatus 101.
Moreover, the web W which is sent out of the lead-in roller 2 and the nip roller 3 forms an air loop 4 with some slack, an amount of which slack within the air loop 4 is monitored by slack amount detecting units 36a-36d, which include optical sensors arranged in multiple steps, and the lead-in roller 2 is driven and controlled such that the amount of slack becomes constant.
The web W which has passed through the air loop 4 passes between a path shaft 5 and an edge guide 6. Two path shafts 5 are arranged in a direction which is orthogonal to a conveying direction of the web W, which passes between the path shafts 5 in an S shape. A pair of edge guides 6 is supported by the path shafts 5 and a dimension of a gap between the edge guides 6 is set generally the same as a width dimension of the web W. Therefore, a running position of the web W in a width direction can be regulated.
The edge guide 6 is fixed to the path shaft 5 with a screw, for example, so that a position thereof can be adjusted in accordance with a width dimension of the web W used.
Prior to a stage in which the web W, which has passed between the path shafts 5 and the edge guides 6, is sent into a feed nip roller 9 which is pressed against by an in feed roller 8 and a spring (not shown), a moderate tension is applied thereto in order to suppress folding or crawling. In the example shown, winding friction is added to a tension shaft 7. The infeed roller 8 is rotationally driven by a driving source (not shown) such as a motor, etc., and conveys the web in cooperation with the feed nip roller 9.
The web W which has passed through the infeed roller 8 is wound around in a U shape from the bottom side of a single first dancer roller 10, which is rotatable. The first dancer roller 10 is rotatably mounted on a first movable frame 11 via a bearing (not shown) which is provided at a roller end portion. Therefore, an encompassing first dancer roller mechanism 12 is hung by the web W.
This first dancer roller mechanism 12 can be moved along gravity directions (upward and downward directions) A. Also are provided first dancer roller mechanism position detecting units 37a to 37d which detect a position of the first dancer roller mechanism 12; in accordance with an output of the position detecting units 37a to 37d, a driving source of the infeed roller 8 may be controlled to increase or decrease speed to regulate a position of the first dancer roller mechanism 12.
The web W, which has passed through the first dancer roller mechanism 12, successively passes through a front face applying unit 13f which applies on the front face side thereof a treatment agent and a back face applying unit 13r which applies on the back face thereof the treatment agent, so that the treatment agent is applied on both faces of the web W. The treatment agent applying unit 13 is not substantially relevant to the present invention, so that an explanation thereof is omitted.
The web W which has passed through the back face applying unit 13r passes through an out feed roller 14 which is rotationally driven by a driving source (not shown) such as a motor, etc., and another feed nip roller 9 which is pushed to the outfeed roller 14 side by a spring (not shown). The outfeed roller 14 is rotationally driven by a driving source (not shown) such as a motor, etc., and conveys the web W in cooperation with the other feed nip roller 9.
Next, the web W is wound, in a W shape, around two second dancer rollers 15a and 15b, which are rotatable, and a guide roller 1 which is arranged between the dancer rollers 15a and 15b. The two dancer rollers 15a and 15b are rotatably mounted to a second movable frame 16 via a bearing (not shown) which is provided to a roller end portion to configure a second dancer roller mechanism 17. Therefore, this second dancer roller mechanism 17 is hung by the web W.
This second dancer roller mechanism 17 is also movable along gravity directions (upward and downward directions) A, and also provided are multiple-step second dancer roller mechanism position detecting units 38a-38d, which detect a position of the second dancer roller mechanism 17, so that a driving source of the out feed roller 14 may be controlled to increase or decrease speed in accordance with an output of the position detecting units 38a to 38d to regulate a position of the second dancer roller mechanism 17.
In this way, the web W, which has passed within the treatment agent applying apparatus 101, is sent into the first inkjet printer 102 on the downstream side as shown in FIG. 7.
Here, with respect to the in feed roller 8 and the out feed roller 14, it is difficult to cause the web conveying speeds thereof to completely match due to a rotational speed error, etc., of a driving source (not shown) or a machining error of a roller diameter. Therefore, a difference of the web conveying speeds can be absorbed by a buffer function of the first dancer roller mechanism 12 to perform continuous conveying.
In other words, if a rise in a position of the first dancer roller mechanism 12 is detected, driving and control are performed such that a rotational speed of the in feed roller 8 which is positioned on the upstream thereof is increased to lower the position of the first dancer roller mechanism 12. Conversely, if a drop in a position of the first dancer roller mechanism 12 is detected, driving and control are performed such that a rotational speed of the in feed roller 8 is decreased to raise the position of the first dancer roller mechanism 12.
Similarly, the second dancer roller mechanism 17 also absorbs a difference in a web conveying speed between a conveying roller (not shown) which determines a web sending-in speed within the first inkjet printer 102 and the outfeed roller 14.
Moreover, the first dancer roller mechanism 12 and the second dancer roller mechanism 17 apply tension to the web W with weights thereof, so that, for the first dancer roller mechanism 12, the tension which is applied to the web W is one half the mechanism weight since it is hung by the web W which is wound around in a U shape, while, for the second dancer roller mechanism 17, the tension which is applied to the web W is one fourth the mechanism weight since it is hung by the web W which is wound around in a W shape.
A related-art dancer roller mechanism has a buffer function, so that a path of the web W becomes complex as shown in the second dancer roller mechanism 17 in FIG. 8, etc.
Leaving the path complex causes loading of the web W to be difficult, so that there is commercialized an apparatus, wherein, at the time of loading the web, as shown in FIG. 9, the first dancer roller mechanism 12 and the second dancer roller mechanism 17 are raised and a length of a path which continues to the guide roller 1 is shortened to improve operability of web loading.
FIG. 10A is a schematic configuration diagram of a dancer roller apparatus as viewed from the front face; and FIG. 10B is a schematic configuration diagram for explaining a driving system of the dancer roller apparatus as viewed from the side face.
As shown in FIGS. 10A and 10B, two rail shafts 20 are arranged with a predetermined gap along gravity directions (upward and downward directions) A, between which two rail shafts 20 the second dancer roller mechanism 17 is arranged. As shown in FIG. 10A, on the side face of the movable frame 16 is fixed a multiple number (three in this example) of shaft guides 19, among which the rail shaft 20 is placed.
Moreover, the second movable frame 16 is connected to a timing belt 23 by a belt clamper 21. The timing belt 23 is stretched between timing pulleys 22a and 22b which are respectively placed thereabove and therebelow, while the timing pulleys 22a and 22b are respectively fixed with keys (not shown), etc., to both ends of elevating axles 24a and 24b. 
The timing pulley 22a which is supported at one end of the elevating axle 24a is connected to a motor 30 via drive transmission gears 25 and 26; a drive axle 27; and drive gears 28 and 29. Therefore, this motor 30 may be rotationally driven to raise or lower the second dancer roller mechanism 17 along the rail shafts 20.
The above-described drive system becomes a load during conveying of the web, so that the dancer roller mechanism 17 affects an operation of absorbing a change in a path length of the web W. In other words, when the drive system becomes the load in the process of the dancer roller mechanism 17 being raised (the path being shortened), a tension applied to the web W increases by an amount corresponding to the load of the drive system in addition to a self weight of the dancer roller mechanism 17.
Conversely, when the drive system becomes the load in the process of the dancer roller mechanism 17 being lowered (the path being lengthened), an operation of the dancer roller mechanism 17 becomes slower, causing the web W to loosen as it cannot follow a change of the path, and causing the web W to become free (without tension).
In order to prevent this, an electromagnetic clutch 31 is provided within a drive transmission system. In an example in FIGS. 10A and 10B, the electromagnetic clutch 31 is arranged between the drive transmission gear 26 and the drive axle 27, and, therefore, when the electromagnetic clutch 31 is turned off during web conveying to separate an operation of the dancer roller mechanism 17 from the drive system, elevating of the dancer roller mechanism 17 causes the elevating axle 24 and the drive transmission gears 25 and 26 to rotationally operate, but the drive axle 27 does not rotate. When forced elevating of the dancer roller mechanism 17 is necessary, such as at the time of web loading, the electromagnetic clutch 31 is turned ON to connect the drive system and the dancer roller mechanism 17 and the motor 30 is rotationally driven to cause an elevating operation of the dancer roller mechanism 17.
A configuration, a control operation, etc., of the dancer roller apparatus are described in below-described Patent Documents 1 to 3, for example.